Powder delivery for additive manufacturing

ABSTRACT

An apparatus includes a platen and a dispensing system overlying the platen. The dispensing system includes a powder source. The dispensing system further includes a powder conveyor extending over the top surface of the platen, rings arranged coaxially along a longitudinal axis of the powder conveyor, and a cap plate extending along a length of the tube. The powder conveyor is configured to receive powder from the powder source. The powder conveyor is configured to move the powder. The rings form a tube surrounding the powder conveyor to contain the powder. Each concentric ring includes a ring opening. Each ring is configured to be independently rotatable. The cap plate includes a cap plate opening. The powder is dispensed from the tube through the ring opening and the cap plate opening when the ring opening and the cap plate opening are aligned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/262,673, filed on Dec. 3, 2015, and claims priority to U.S.Provisional Application Ser. No. 62/219,605, filed Sep. 16, 2015, theentirety of each being incorporated by reference.

TECHNICAL FIELD

This specification relates to additive manufacturing, also known as 3Dprinting.

BACKGROUND

Additive manufacturing (AM), also known as solid freeform fabrication or3D printing, refers to a manufacturing process where three-dimensionalobjects are built up from successive dispensing of raw material (e.g.,powders, liquids, suspensions, or molten solids) into two-dimensionallayers. In contrast, traditional machining techniques involvesubtractive processes in which objects are cut out from a stock material(e.g., a block of wood, plastic or metal).

A variety of additive processes can be used in additive manufacturing.Some methods melt or soften material to produce layers, e.g., selectivelaser melting (SLM) or direct metal laser sintering (DMLS), selectivelaser sintering (SLS), fused deposition modeling (FDM), while otherscure liquid materials using different technologies, e.g.,stereolithography (SLA). These processes can differ in the way layersare formed to create the finished objects and in the materials that arecompatible for use in the processes.

Conventional systems use an energy source for sintering or melting apowdered material. Once all the selected locations on the first layerare sintered or melted and then re-solidified, a new layer of powderedmaterial is deposited on top of the completed layer, and the process isrepeated layer by layer until the desired object is produced.

SUMMARY

In one aspect, an additive manufacturing apparatus for forming an objectincludes a platen to support the object being formed, a dispensingsystem overlying the platen, and an energy source to apply energy to thepowder dispensed on the top surface of the platen to form a fusedportion of the powder. The dispensing system includes a powder sourceconfigured to hold powder to be dispensed over a top surface of theplaten and a powder conveyor extending over the top surface of theplaten. The powder conveyor includes a proximal end configured toreceive the powder from the powder source. The powder conveyor isconfigured to move the powder carried within the powder conveyor along alength of the powder conveyor. The dispensing system also includes ringsarranged coaxially along a longitudinal axis of the powder conveyor. Therings form a tube surrounding the powder conveyor and are configured tocontain the powder. Each concentric ring includes at least one ringopening. The dispensing system also includes a cap plate extending alonga length of the tube. The cap plate includes at least one cap plateopening. Each ring is configured to be independently rotatable such thatthe at least one ring opening of the respective concentric ring ismovable into or out of alignment with the at least one cap plateopening. The powder is dispensed from the tube through the at least onering opening and the at least one cap plate opening when the at leastone ring opening and the at least one cap plate opening are aligned.

Features can include one or more of the following. The powder conveyorcan be rotatable about the longitudinal axis of the powder conveyor tomove the powder carried within the powder conveyor along the length ofthe powder conveyor. The powder conveyor can further include a screwconveyor coaxial with the longitudinal axis of the powder conveyor androtatable about the longitudinal axis of the powder conveyor such that,when the screw conveyor rotates, the screw conveyor moves the powdercarried within the powder conveyor along the length of the powderconveyor.

The screw conveyor can be configured such that when the screw conveyorrotates in a first direction about the longitudinal axis, the screwconveyor carries the powder along the longitudinal axis away from theproximal end of the powder conveyor. The screw conveyor can be furtherconfigured such that when the screw conveyor rotates in a seconddirection about the longitudinal axis, the screw conveyor carries thepowder along the longitudinal axis toward the proximal end of the powderconveyor. The additive manufacturing apparatus can further include amotor to drive the screw conveyor and controller coupled to the motor.The controller can be configured to cause the screw conveyor toalternate between the rotation in the first direction and the seconddirection during dispensing of the powder to form the object. The screwconveyor can be configured to compact the powder when the screw conveyorrotates in the first direction. The controller can be configured tocause the screw conveyor to, prior to the dispensing, rotate in thefirst direction until powder extends along substantially all of thetube.

Each ring can include two or more positions spaced angularly around thering, each position having one or more openings and having a distinctcombination of a number of openings and opening size. Each ring can bemovable between the positions such that a different position is alignedwith the at least one cap plate opening. The combination can furtherdefine the at least one cap plate opening of each concentric ring. Thecombination can further include a number of openings of and a positionof the at least one cap plate opening for each concentric ring.

A distal end of the powder conveyor can extend over the top surface ofthe platen. The distal end of the powder conveyor can be closed toprevent the powder from exiting the powder conveyor through the distalend. At least one cap plate opening can include a slot extending along alongitudinal axis of the cap plate. At least one cap plate opening caninclude two or more openings for each ring. The tube can surround thecap plate, or the cap plate can surround the tube.

A drive system of each concentric ring can include a motor with arotational axis offset from and parallel to the longitudinal axis of thepowder conveyor. The drive system can further include a linkage systemconnected to the motor such that rotation of the motor about itsrotational axis causes rotation of the concentric ring about thelongitudinal axis of the powder conveyor. The motor of the drive systemof each of the concentric rings can include a distinct shaft length. Adrive system of each concentric ring can include a solenoid configuredto generate an electromagnetic field to rotate the concentric ring aboutthe longitudinal axis of the auger conveyor.

The dispensing system can be a first dispensing system. The powder canbe a first powder. The additive manufacturing apparatus can furtherinclude a second dispensing system configured to receive a second powderto be dispensed over the top surface of the platen. The second powdercan include a diameter small than a diameter of the first powder.

The energy source can include heaters configured to apply the energy tothe powder. The heater can be addressable such that that the energy isselectively applied to the powder dispensed through the at least onering opening and the concentric at least one cap plate opening.

In a further aspect, a dispensing system includes a powder sourceconfigured to hold powder to be dispensed over a top surface of aplaten. The dispensing system further includes a powder conveyorextending over the top surface of the platen. The powder conveyorincludes a proximal end configured to receive the powder from the powdersource. The powder conveyor is configured to move the powder carriedwithin the powder conveyor along a length of the powder conveyor. Thedispensing system includes rings arranged coaxially along a longitudinalaxis of the powder conveyor. The rings form a tube surrounding thepowder conveyor and configured to contain the powder. Each concentricring includes at least one ring opening. The dispensing system includesa cap plate extending along a length of the tube. The cap plate includesat least one cap plate opening. Each ring is configured to beindependently rotatable such that the at least one ring opening of therespective concentric ring is movable into or out of alignment with theat least one cap plate opening. The powder is dispensed from the tubethrough the at least one ring opening and the at least one cap plateopening when the at least one ring opening and the at least one capplate opening are aligned.

Advantages of the foregoing may include, but are not limited to, thefollowing. The efficiency of forming an object and increase overallthroughput of additive manufacturing can be increased. The dispensingsystem can include several paths through which powder can be dispensedin parallel onto a platform of the additive manufacturing apparatus.These multiple available paths can be independently controlled such thatthe placement of powder onto the build platform can be controlled.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other potential features, aspects,and advantages will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic side view of an example of an additivemanufacturing apparatus.

FIG. 1B is a schematic top view of the additive manufacturing apparatusof FIG. 1A.

FIG. 2 is a front perspective cutaway view of a printhead.

FIG. 3A is a front-side perspective view of a dispensing system.

FIG. 3B is a front-side perspective cross-sectional view of thedispensing system of FIG. 3A.

FIG. 3C is an enlarged front-side perspective cross-sectional view ofthe dispensing system of FIG. 3A.

FIG. 3D is a bottom view of the dispensing system of FIG. 3A.

FIG. 3E is a front view of the dispensing system of FIG. 3A.

FIG. 3F is a top view of the dispensing system of FIG. 3A.

FIG. 3G is an enlarged top cutaway view of a powder conveyor for thedispensing system of FIG. 3A.

FIG. 4A is a bottom perspective view of a ring for a dispensing system.

FIG. 4B is a bottom view of the ring of FIG. 4A.

FIG. 5A is a bottom perspective view of a cap plate for a dispensingsystem.

FIG. 5B is a bottom view of the cap plate of FIG. 5A.

FIGS. 6A to 6F are front cross-sectional views of differentconfigurations of a cap plate and a ring for a dispensing system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Additive manufacturing (AM) apparatuses can form an object by dispensingand fusing successive layers of a powder on a build platform. Control ofthe area on the build stage on which powder is dispensed is desirable.For example, a controllable dispenser can permit control of the geometryof the object, or simply be used to avoid dispensing powder in areas ofthe build platform that will not support the object, thus reducing theconsumption of powder.

The dispensing system described below can include controllable andmovable structures that enable the apparatus to selectively dispense thepowder on the build platform. Optionally, the dispensing system'scontrollable and movable structures also enable control of the powderdispensing rate, which can be selected to be low for localized andprecise dispensing or can be selected to be high for high-throughputdispensing.

Additive Manufacturing Apparatuses

FIG. 1A shows a schematic side view of an example additive manufacturing(AM) apparatus 100 that includes a dispensing system for dispensing ofpowder to form an object during a build operation. The apparatus 100includes a printhead 102 and a build platform 104 (e.g., a build stage).The printhead 102 dispenses a powder 106 and, optionally, fuses thepowder 106 dispensed on the platform 104. Optionally, as describedbelow, the printhead 102 can also dispense and/or fuse a second powder108 on the platform 104.

Referring to FIGS. 1A and 1B, the printhead 102 is supported on a gantry110 (e.g., a platform, a support) configured to traverse the platform104. The gantry 110 can include a horizontally extending support onwhich the printheads are mounted. For example, the gantry 110 can bedriven along rails 119 by a linear actuator and/or motor so as to moveacross the platform 104 along a first axis parallel to a forwarddirection 109. In some implementations, the printhead 102 can move alongthe gantry 110 along a horizontal second axis 115 perpendicular to thefirst axis. Movement along both the first and second axes enables theprinthead 102 and its systems to reach different parts of the platform104 beneath the gantry 110. The movement of the printhead 102 along thegantry 110 and the movement of the gantry 110 along the rails 119provide multiple degrees of freedom of mobility for the printhead 102.The printhead 102 can move along a plane above and parallel to the buildplatform 104 such that the printhead 102 can be selectively positionedabove a usable area of the build platform 104 (e.g., an area where thepowder can be dispensed and fused).

The printhead 102 and the gantry 110 can cooperate to scan the usablearea of the build platform 104, enabling the printhead 102 to dispensepowder along the build platform 104 as needed to form the object. In theexample as shown in FIG. 1B, the printhead 102 can scan in the forwarddirection 109 along the build platform 104. After the printhead 102travels across the build platform 104 from a first end 111 to a secondend 113 of the build platform 104 for a first time to deposit a firststripe of the layer of powder. Then the printhead 102 can return to thefirst end 111, move in a lateral direction along the horizontal secondaxis 115, and begin a travel across the build platform 104 again in theforward direction 109 for a second time to deposit a second stripe onthe build platform 104 that is parallel to the first stripe. If theprinthead 102 dispenses two or more different sizes of powder, theprinthead 102 can dispense the two or more different powders during asingle pass across the platform 104.

Alternatively, the gantry 110 can include two or more printheads thatspan the width of the platform 104. In this case, motion of theprinthead 102 in the lateral direction along the horizontal second axis115 may not be needed.

Referring to FIG. 1A and to FIG. 2, which shows a cutaway view of theprinthead 102 the printhead 102 includes at least a first dispensingsystem 116 to selectively dispense powder 106 on the build platform 104.

The apparatus 100 also includes an energy source 114 to selectively addenergy to the layer of powder on the build platform 104. The energysource 114 can be incorporated into the printhead 102, mounted on thegantry 110, or be mounted separately, e.g., on a frame supporting thebuild platform 104 or on chamber wall that surrounds the build platform104.

In some implementations, the energy source 114 can include a scanninglaser that generates a beam of focused energy that increases atemperature of a small area of the layer of the powder. The energysource 114 can fuse the powder by using, for example, a sinteringprocess, a melting process, or other process to cause the powder to forma solid mass of material. In some cases, the energy source 114 caninclude an ion beam or an electron beam.

The energy sources 114 can be positioned on the printhead 102 such that,as the printhead 102 advances in the forward direction 109, the energysources can cover lines of powder dispensed by the dispensing system116. When the apparatus 100 includes multiple dispensing systems, theprinthead 102 can also optionally include an energy source for each ofthe dispensing systems. If the apparatus includes multiple heat sources,the energy sources can each be located immediately ahead of one of theheat sources.

Optionally, the apparatus can include a heat source 112 to direct heatto raise the temperature of the deposited powder. The heat source 112can heat the deposited powder to a temperature that is below itssintering or melting temperature. The heat source 112 can be, forexample, a heat lamp array. The energy source 114 can be incorporatedinto the printhead 102, mounted on the gantry 110, or be mountedseparately, e.g., on a frame supporting the build platform 104 or onchamber wall that surrounds the build platform 104. The heat source 112can be located, relative to the forward moving direction 109 of theprinthead 102, behind the first dispensing system 116. As the printhead102 moves in the forward direction 109, the heat source 112 moves acrossthe area where the first dispensing system 116 was previously located.

In some implementations, the heat source 112 is a digitally addressableheat source in the form of an array of individually controllable lightsources. The array includes, for example, vertical-cavitysurface-emitting laser (VCSEL) chips, positioned above the platform 104.The array can be within the printhead 102 or be separate from theprinthead 102. The array of controllable light sources can be a lineararray driven by an actuator of a drive system to scan across theplatform 104. In some cases, the array is a full two-dimensional arraythat selectively heats regions of the layer by activating a subset ofthe individually controllable light sources. Alternatively or inaddition, the heat source includes a lamp array to simultaneously heatthe entire layer of the powder. The lamp array can be part of theprinthead 102 or can be an independent heat source unit that is part ofthe apparatus 100 but separate from the printhead 102.

In some implementations, the build platform 104 may include a heaterthat can heat powder dispensed on the build platform 104. The heater canbe an alternative to or in addition to the heat source 112 of theprinthead 102.

Optionally, the printhead 102 and/or the gantry 110 can also include afirst spreader 118, e.g., a roller or blade, that cooperates with firstthe dispensing system 116 to compact and spread powder dispensed by thedispensing system 116. The spreader 118 can provide the layer with asubstantially uniform thickness. In some cases, the first spreader 118can press on the layer of powder to compact the powder.

The printhead 102 and/or the gantry 110 can also optionally include afirst sensing system 120 and/or a second sensing system 122 to detectproperties of the apparatus 100 as well as powder dispensed by thedispensing system 116.

In some implementations, the printhead 102 includes a second dispensingsystem 124 to dispense the second powder 108. A second spreader 126 canoperate with the second dispensing system 124 to spread and compact thesecond powder 108. The apparatus 100, e.g., the printhead 102 or thegantry 110, can also include a second heat source 125 that, like thefirst heat source 112, directs heat to powder in large areas of thebuild platform 104.

A controller 128 can coordinate the operations of the energy source 114,heat source 112 (if present), and dispensing system 116. The controller128 can operate the dispensing system 116 to dispense the powder 106 andcan operate the energy source 114 and the heat source 112 to fuse thepowder 106 to form a workpiece 130 that becomes the object to be formed.

The controller 128 can operate the first dispensing system 116 tocontrol, for example, the thickness and the distribution of the powder106 dispensed on the build platform 104. The thickness of each layerdepends on, for example, the number of the powder particles 106 stackedthrough a height of the layer or the mean diameter of the powderparticles 106. In some implementations, each layer of the powderparticles 106 is a single particle thick. In some cases, each layer hasa thickness resulting from stacking multiple powder particles 106 on topof each other.

In some implementations, the height of the layer also depends on adistribution density of the powder particles 106, e.g., how closelypacked the powder particles 106 are. A level of compaction of the powder106 can affect the thickness of each layer dispensed. Higher levels ofcompaction of the powder 106 can reduce the thickness of the layerdispensed as compared to a layer formed with the same number ofparticles at a lower level of compaction. The higher level of compactioncan further increase a uniformity of the thickness across the layer andreduce the laser residency time need to melt the layer. The thickness ofeach layer and the compaction of the powder can be selected to control adesired resolution for the geometry of the portion of the object beingformed in that layer.

The distribution of powder dispensed for each layer, e.g., the locationsof the powder within each layer, can vary based on the implementation ofthe additive manufacturing apparatus. In some cases, the firstdispensing system 116 can selectively dispense a layer of powders acrossthe build stage such that some portions include powder and some portionsdo not include powder. In some implementations, the first dispensingsystem 116 can dispense a uniform layer of materials on the worksurface.

Referring to FIG. 2, the first dispensing system 116 receives the powder106 in a powder hopper 131. The powder 106 then travels through achannel 136. The powder hopper 131 can be filled with powder such thatthe powder hopper 131 serves as a powder source for the channel 136during a dispensing operation. The first dispensing system 116 dispensesthe powder 106 onto the build platform 104 through one or more ofseveral available openings or holes extending from the channel 136. Theholes or openings can be selectively openable. In particular, thechannel 136 can be formed by selectively controllable and movable rings,e.g., rotatable rings, that include the openings. The rings, togetherwhen stacked along their common central cylindrical axis, can be in theshape of a tube with the channel 136 corresponding to the aperturethrough the tube. As the rings rotate, the openings move angularlyaround the common cylindrical axis.

The controller 128 can selectively actuate ring drive mechanisms 138 tocontrol the ring through which powder is dispensed. In cases where eachring includes multiple openings, the controller can also actuate each ofthe ring drive mechanisms 138 to select one or more of the multipleopenings through which to dispense powder.

Each group of opening at a particular angular location on a ring can besized and dimensioned such that the powder is dispensed at a differentrate. The rotation of the rings, and hence, the selection of the openingor openings through which the powder is dispensed, enable the controller128 to select a rate at which the powder is dispensed onto the buildplatform 104.

Using the first dispensing system 116, the controller can control thepowder's distribution on the build platform 104 and distribution. Thefirst dispensing system 116 can control a distribution of the powder ina layer dispensed on the build platform 104 or on an uppermost layer ofpowder. In some cases, the first dispensing system 116 can dispense thepowder through one of the openings to achieve selective dispensing ofthe powder onto the build platform 104 or the uppermost layer of powder.In some cases, the first dispensing system 116 can dispense the powderthrough more than one opening (e.g., through a hole in each of therings) so that the first dispensing system 116 can dispense powderacross a larger area of the build platform 104 at once.

The first spreader 118 can then spread the powder across the buildplatform 104. The spreader can provide the layer with a substantiallyuniform thickness. In some implementations, the first spreader 118 is ablade that translates across the platform 104. In some cases, the firstspreader 118 is a roller or rotating cylinder that rolls across theplatform 104. The spreader 118 can roll in a clockwise direction and/ora counterclockwise direction.

Optionally, the printhead can include a second dispensing system 124 todeliver a second powder. The second dispensing system 124 receives thepowder 108 in a powder hopper 134. The powder 108 then travels through achannel 136. Similar to the first dispensing system 116, the seconddispensing system 124 can control the rate at which powder is dispensedthrough the build platform 104 by rotating rings containing holesthrough which the powder is dispensed. The second dispensing system 124can also compact the powder so that powder dispensed from the firstdispensing system 116 has a desired distribution density.

If present, the second dispensing system 124 enables delivery of asecond type of powder 108 having properties different than the firstpowder 106. The first powder particles 106 can have a larger meandiameter than the second particle particles 108, e.g., by a factor oftwo or more. When the second powder particles 108 are dispensed on alayer of the first powder particles 106, the second powder particles 108infiltrate the layer of first powder particles 106 to fill voids betweenthe first powder particles 106. The second powder particles 108, beingsmaller than the first powder particles 106, can achieve a higherresolution, higher pre-sintering density, and/or a higher compactionrate.

Alternatively or in addition, if the apparatus 100 includes two types ofpowders, the first powder particles 106 can have a different sinteringtemperature than the second powder particles. For example, the firstpowder can have a lower sintering temperature than the second powder. Insuch implementations, the energy source 114 can be used to heat theentire layer of powder to a temperature such that the first particlesfuse but the second powder does not fuse.

In some implementations, the controller 128 can control the first andsecond dispensing systems 116, 124 to selectively deliver the first andthe second powder particles 106, 108 to different regions.

In implementations when multiples types of powders are used, the firstand second dispensing systems 116, 124 can deliver the first and thesecond powder particles 106, 108 each into selected areas, depending onthe resolution requirement of the portion of the object to be formed.

Materials for the powder include metals, such as, for example, steel,aluminum, cobalt, chrome, and titanium, alloy mixtures, ceramics,composites, and green sand. In implementations with two different typesof powders, in some cases, the first and second powder particles 106,108 can be formed of different materials, while, in other cases, thefirst and second powder particles 106, 108 have the same materialcomposition. In an example in which the apparatus 100 is operated toform a metal object and dispenses two types of powder, the first andsecond powder particles 106, 108 can have compositions that combine toform a metal alloy or intermetallic material.

If the apparatus 100 dispenses two different types of powders havingdifferent sintering temperatures, the first and second heat sources 112,125 can have different temperature or heating set points. For example,if the first powder 106 can be sintered at a lower temperature than thesecond powder 108, the first heat source 112 may have a lowertemperature set point than the second heat source 125.

In some implementations, the building platform 104 is fixed and theprinthead 102 moves in a vertical direction to dispense successivelayers of the powder. In some implementations, the build platform 104can be moved upward or downward during build operations. For example,the build platform 104 can be moved downward with each layer dispensedby the first dispensing system 116 so that the printhead 102 can remainat the same vertical height with each successive layer dispensed. Thecontroller 128 can operate a drive mechanism, e.g., a piston or linearactuator, connected to the build platform 104 to decrease a height ofthe build platform 104 so that the build platform 104 can be moved awayfrom the printhead 102. Alternatively, the build platform 104 can beheld in a fixed vertical position, and the gantry 110 can be raisedafter each layer is deposited.

The controller 128 controls the operations of the apparatus 100,including the operations of the printhead 102 and its subsystems, suchas the heat source 112, the energy source 114, and the first dispensingsystem 116. The controller 128 can also control, if present, the firstspreader 118, the first sensing system 120, the second sensing system122, the second dispensing system 124, and the second spreader 126. Thecontroller 128 can also receive signals from, for example, user input ona user interface of the apparatus or sensing signals from sensors of theapparatus 100.

The controller 128 can include a computer aided design (CAD) system thatreceives and/or generates CAD data. The CAD data is indicative of theobject to be formed, and, as described herein, can be used to determineproperties of the structures formed during additive manufacturingprocesses. Based on the CAD data, the controller 128 can generateinstructions usable by each of the systems operable with the controller128, for example, to dispense the powder 106, to fuse the powder 106, tomove various systems of the apparatus 100, and to sense properties ofthe systems, powder, and/or the workpiece 130.

The controller 128, for example, can transmit control signals to drivemechanisms that move various components of the apparatus. In someimplementations, the drive mechanisms can cause translation and/orrotation of these different systems, including dispensers, rollers,support plates, energy sources, heat sources, sensing systems, sensors,and other components of the apparatus 100. Each of the drive mechanismscan include one or more actuators, linkages, and other mechanical orelectromechanical parts to enable movement of the components of theapparatus.

The controller 128, in some cases, controls movement of the printhead102 and can also control movements of individual systems of theprinthead 102. For example, the controller 128 can cause the printhead102 to move to a particular location along the gantry 110, and thecontroller 128 can transmit a separate control signal to drive aseparate drive mechanism to move the energy source 114 of the printhead102 along the printhead 102. The apparatus 100 can further include adrive mechanism that moves the gantry 110 along the build platform 104so that the printhead 102 can be positioned above different areas of thebuild platform 104.

The controller 128 can also control individual structures of thedispensing system 116, including the movable and controllable ringsdescribed herein and a powder conveyor contained within the dispensingsystem 116. The controller 128 can control the dispensing system 116 toadjust delivery rates of the powder, a level of compaction of thepowder, as well as the locations on the build platform 104 where thepowder is dispensed.

Dispensing Systems

FIGS. 3A to 3G depict various views of the dispensing system 116(and/or, e.g., the second dispensing system 124). As shown in theperspective view of the dispensing system 116 shown in FIG. 3A, thedispensing system 116 includes the powder hopper 131 to receive powderto be dispensed (and possibly compacted) by the dispensing system 116.

Also referring to FIG. 3B depicting a perspective cross-sectional viewof the dispensing system 116, powder travels through the powder hopper131 into the channel 136. A conveyor drive mechanism 139 of thedispensing system 116 can drive a powder conveyor 140 that causes thepowder to move between an entrance 142 of the channel 136 and a closedend 144 of the channel 136. The powder conveyor 140 can be an augerscrew.

The conveyor 140 can rotate to carry the powder within the channel 136.For example, rotation of an auger screw can drive powder forward throughthe channel 136.

In some implementations, the conveyor 140, instead of rotating,translates along the channel 136 to distribute the powder within thechannel 136. In some implementations, the conveyor 140 oscillates orvibrates to distribute the powder within the channel 136.

In some implementations, the conveyor drive mechanism 139 can include adrive motor 141. The drive motor 141 can be a high torque drive motorthat enables the conveyor drive mechanism 139 to cause the conveyor 140to exert high levels of pressure on powder within the channel 136. Insome implementations, the drive mechanism 139 can further include gears,linkages, and other force and torque transfer devices that transfer thetorque from the drive motor to the conveyor 140.

Referring to FIG. 3C, which shows an enlarged perspectivecross-sectional view of the channel 136 of the dispensing system 116. Aseries of annular rings 146 encircle the conveyor 140. The aperturesthrough the rings 146 define the channel 136 through which the powdertravels. In particular, an inside surface of the rings 146 form thechannel 136. Thus, as powder is travelling through the channel 136, thepowder contacts the inside surface of the rings 146. The annular rings146 each have a center that is concentric with a longitudinal axis 162of the conveyor 140. In some implementations, the conveyor 140 rotatesabout this longitudinal axis 162 to move the powder through the channel136.

As shown in FIGS. 4A and 4B, which are a bottom perspective view and abottom view, respectively, of an example of the ring 146, each of therings 146 includes an opening 148 that goes through the ring 146 fromthe inside surface to an outside surface of the ring 146.

In some implementations, each of the rings 146 includes multipleopenings 148 spaced at different angular positions around the ring 146.The openings 148 can vary in size, shape, and quantity. For example,each of the rings 146 can include multiple openings of different sizes.In some cases, one or more of different angular positions on the ring146 can include multiple openings. While three openings 148 are shown inFIGS. 4A and 4B, in some cases, a ring 146 could have just two, or fouror more openings, each having a different size. Each ring can have thesame pattern of openings. In some cases, the rings 146 each have asingle opening 148 of the same size. For circular openings 148, thediameter of the openings 148 can be between, for example, 10 micrometersand 100 micrometers.

Also referring to FIG. 3D, showing a bottom view of the dispensingsystem 116, a cap plate 150 is positioned beneath the rings 146. The capplate 150 extends along the channel 136 and extends along a combinedlength of the portion of the channel 136 provided by the rings 146. Thecap plate includes openings 152. Each of the openings 152 of the capplate 150 can correspond a different one of the rings 146. The openingscan be arranged on line parallel to the longitudinal axis.

Each opening 152 can be larger or smaller than the opening 148 of thecorresponding ring 146. In some cases, as shown in FIGS. 5A and 5B,which show a bottom perspective view and a bottom view of an example ofthe cap plate 150, all of the openings 152 can have the same size. Theopenings 152 can be aligned with one another and evenly spaced apart.

While described as circular openings, the openings 148 and the openings152 can be slots, slits, or other appropriate shapes. In some cases, theopenings 148 and/or the openings 152 can be rectangular or oval.Although the cap plate 150 has been described to include several capplate openings 152 with at least one cap plate opening for each ring146, in some cases, the cap plate 150 includes a single slot thatextends beneath all or several of the rings. The slot can extendparallel to the longitudinal axis of the channel. For example, the capplate 150 could include two or more slots, each slot corresponding totwo or more of the rings. In some cases, the cap plate includes one slotextending across all of the rings. In some implementations, the slot hasa uniform width, while in other cases, the slots vary in width.

The rings 146 are adjacent to and above the cap plate 150, so theopenings 148 of the rings 146 can be aligned with the openings 152 ofthe cap plate 150. In particular, each ring 146 can be rotated such thatits opening 148 can align with its corresponding opening in the capplate 150. FIG. 3E shows a front cross-sectional view of the dispensingsystem 116, and FIG. 3F shows a top cross-sectional view of thedispensing system 116. The dispensing system 116 includes ring drivemechanisms 138, each of which are connected to a corresponding one ofthe rings 146.

In some implementations, each of the ring drive mechanisms 138 caninclude a motor 156 and a linkage system 158 such that the motor cancause one of the rings 146 to rotate. The linkage system 158 can includegears, linkages, arms, and other force and torque transmitting elementsto transfer the torque of the motor 156 into a rotational force on itsassociated ring 146. The motor 156 can be operated to rotate itsassociated ring 146 in both directions about its center. In someimplementations, shaft lengths of the motors 156 can vary such that themotors 156 can each be mounted onto the same planar surface. In someimplementations, each of the ring drive mechanisms 138 or each of themotors 156 can operate two or more of the rings 146 to rotate two ormore of the rings simultaneously.

The ring drive mechanisms 138 rotate the rings 146 about the centers ofthe rings 146. The center of the rings 146 can coincide with thelongitudinal axis 162 of the conveyor 140. Thus, as the rings 146rotate, the channel 136 formed by the rings 146 can remain substantiallythe shape and size.

In some implementations, the rings are driven by a magnetic drivemechanism. The magnetic drive mechanism can rotate the rings. In somecases, the magnetic drive mechanism closes or opens an opening of thering depending on a polarity of the magnetic drive mechanism. Themagnetic drive mechanism can include a solenoid. The controller cancontrol the solenoid to generate an electromagnetic field that interactswith magnetic or ferromagnetic material of one of the rings 146. Theelectromagnetic field can drive the ring 146 about the longitudinal axis162 of the conveyor 140.

For each ring 146, the controller (e.g., the controller 128 of theapparatus 100 shown in FIG. 1B) can control the corresponding ring drivemechanism 138 of the ring 146 to set a rotational position of the ring146. The rotational position of the ring 146 determines the position ofthe opening 148 of the ring 146 relative to the corresponding opening152 of the cap plate 150. In the examples shown and described withrespect to FIGS. 4A, 4B, 5A, and 5B, each ring 146 has multiple openings148 and has one corresponding opening 152 in the cap plate 150.

The controller can operate one of the ring drive mechanisms 138 todispense powder from the ring 146 associated with that ring drivemechanism 138. The controller can operate the ring drive mechanism 138to rotate the ring 146 such that one of the openings 148 of the ring 146aligns with its corresponding opening 152 in the cap plate 150. When theopening 148 is aligned with the corresponding opening 152, powdertravelling through the channel 136 formed by the set of rings 146 cantravel through the opening 148 and the corresponding opening 152. Thatpowder can therefore travel through the cap plate 150 and can bedispensed onto the build platform (e.g., the build platform 104 of theapparatus 100 shown in FIGS. 1A and 1B).

The controller can also operate the ring drive mechanism 138 so thatpowder is not dispensed from the associated ring 146. The controller canalso operate the ring drive mechanism 138 to rotate the ring 146 suchthat the openings 148 of the ring 146 are misaligned with theircorresponding opening in the cap plate 150. When the openings 148 and152 are misaligned, powder in the channel 136 is blocked by the body ofthe cap plate 150 and unable to pass through the ring 146, as theirrespective openings 148, 152 do not provide a path for the powder. Thepowder therefore is not dispensed from the portion of the channel 136corresponding to that ring 146.

In cases where the ring 146 includes multiple openings 148 at differentangular positions around the ring, the controller can select one of theopenings 148 from among the several openings to align to the respectiveopening 152 to control a rate of the powder dispensed from the channel136 through the ring 146. If the multiple openings 148 have differentsizes as shown in FIGS. 4A and 4B, the larger sized openings candispense powder at a greater rate than the smaller sized openings.Similarly, the smaller sized openings can dispense powder at a lowerrate than the larger sized openings. To control the powder dispensingrate from the channel 136, the controller can select which of theopenings 148, among the larger and smaller multiple openings 148, toalign with the corresponding openings 152 of the cap plate 150.

In some implementations, the controller can cause partial alignment ofthe opening 148 and the corresponding opening 152 in the cap plate 150to control the powder dispensing rate. In cases where the ring 146 hasmultiple openings 148, the controller can operate the ring drivemechanism 138 so that one of the openings 148 and the correspondingopening 152 in the cap plate 150 are in a partially aligned positionsrelative to one another. In the partially aligned positions, the opening148 of the ring 146 and the opening 152 of the cap plate enable powderto be dispensed from the portion of the channel 136. However, thepartial alignment can reduce the rate of powder dispensed from thatportion of the channel 136 as compared to the rate of powder dispensedfrom that portion if the opening 148 and the corresponding opening 152were in full alignment. Although the ring 146, for example as shown inFIGS. 4A and 4B, has three openings 148, the controller can select frommore than three powder dispensing rates by partially aligning theopenings 148 with the opening 152 in the cap plate.

In some implementations, the ring 146 may only have a single opening148. In some implementations, even though the ring 146 only has a singleopening, the controller can still modulate the powder dispensing rate bycontrolling an amount of alignment between the single opening 148 andthe opening 152 of the cap plate 150. In some implementations in whichthe ring 146 has only a single opening, the controller is configured tosimply provide a binary on/off state for dispensing of the powder.

The controller can also control the rotational position of each of therings 146 for simultaneous dispensing powder from multiple rings 146. Inparticular, the controller can select multiple rings, and thereforemultiple locations along the channel 136, from which the powder isdispensed. In some cases, the controller can dispense large amounts ofpowder across a wide area. In this regard, the controller can rotateseveral or all of the rings 146 such that their openings 148 are fullyaligned with their corresponding openings 152. In this configuration,the controller can dispense powder from each of the openings 152 of thecap plate 150, thus enabling the dispensing system 116 to dispense largeamounts of powder across a wide area.

In some cases, the controller can dispense a small amount of powder in alocalized or limited area by dispensing powder from a subset of therings 146. The controller can control the subset of the rings 146 sothat their openings 148 are aligned with their corresponding openings152 in the cap plate 150. For the remaining rings 146, the controllercan control them such that their openings 148 are misaligned with thecorresponding openings 152 in the cap plate 150. In this configuration,the dispensing system 116 dispenses powder only through those rings 146who are in the positions in which their openings 148 are aligned withthe corresponding openings 152 in the cap plate 150.

The conveyor 140, which moves the powder to be dispensed through theopenings 152, can be an auger conveyor or screw conveyor with helicalblades 160. The helical blades 160 can be helical screw blades. As thethreads push the powder, the powder can travel along the channel 136.The helical blades 160 can rotate about a longitudinal axis 162 of theauger conveyor, which can be coincident with the centers of the rings146. The conveyor drive mechanism 139 can provide the torque to rotatethe auger conveyor. As the auger conveyor rotates, the helical blades160 push the powder contained in the channel 136 so that the powder cantravel through the channel 136. The auger conveyor can move the powderalong the length of the auger conveyor. In this regard, the augerconveyor can move the powder and enable the powder to be dispensed fromthe different portions of the channel 136 along the length of thechannel 136. These different portions can correspond to the differentring openings 148 and the different cap plate openings 152. In someimplementations, the auger conveyor includes a lead screw in which thethreads serve as the pushing surface for the powder.

The powder can be moved in both directions along the longitudinal axis162 of the conveyor 140. For example, during a dispensing operation, thecontroller can control the auger conveyor to alternate directions ofrotation. This back and forth motion can be more effective in dispensingthe powder.

The controller, in some cases, can control the conveyor 140 to compactthe powder before the powder is dispensed from the channel 136 onto thebuild platform. In some implementations, as shown in FIG. 3G, the end144 of the conveyor 140 can be closed. When the channel 136 is filledwith powder, the conveyor 140 can push the powder toward the end 144without causing bulk movement of the powder. Rather, because the channel136 is filled with the powder, the conveyor 140 can cause compaction ofthe powder.

While FIGS. 4A and 4B depict multiple ring openings 148 of varying sizesfor a particular example of a ring 146 and FIGS. 5A and 5B depict onecap plate opening 152 for each ring 146, in other implementations, thecombination of the number of ring openings, the number of correspondingcap plate openings per ring, the size of the ring openings, and the sizeof the cap plate openings may vary. While FIGS. 5A and 5B depict auniform cap plate opening 152 for each ring 146, in someimplementations, the cap plate opening or openings for each ring canvary in size and quantity from one another. For example, a set of capplate openings for a single ring can include two or more cap plateopenings while another set of cap plate openings for a single ring caninclude only a single cap plate opening.

FIGS. 6A to 6F show front cross-sectional views taken along a sectionline passing through a ring opening or ring openings and a cap plateopening or cap plate openings. These views thus depict the ring openingsor openings for a particular ring 146 and the corresponding cap plateopening or openings in the cap plate 150 for that ring. The ring 146rotates relative to the cap plate 150 about the longitudinal axis 162,e.g., the ring 146 rotates while the cap plate 150 remains stationaryrelative to the dispenser (the entire dispenser can be moving laterallyacross the build platform). As described in greater detail below, therotation of the ring 146 enables powder to be dispensed from the portionof the channel 136 formed by the ring 146. Only one ring 146 is shown ineach of these views, but the channel 136 is defined by a series of ringsthat may have ring openings of varying size and quantity.

In some implementations, the multiple ring openings 148 of a particularring 146 are all smaller than the corresponding cap plate opening 152.The size of the ring openings 148 can thus determine the powderdispensing rate from the ring 146. In some cases, as shown in FIG. 6A,some of the ring openings of a ring 146 are smaller than thecorresponding cap plate opening, while some of the ring openings of thering 146 are larger than the corresponding cap plate opening 152. Inparticular, ring openings 600A and 605A are smaller than the cap plateopening 615A, and the ring opening 610A is larger than the cap plateopening 615A. When either the ring opening 600A or the ring opening 605Ais aligned with the cap plate opening 615A, the powder dispensing ratecan be proportional to a size of the ring openings 600A, 600B (e.g., anarea of the openings 600A, 600B). In contrast, when the ring opening610A is aligned with the cap plate opening 615A, because the cap plateopening 615A is smaller than the ring opening 610A, the powderdispensing rate is based on a size of the cap plate opening 615A. Thecap plate opening 615A can thus determine an upper limit for a powderdispensing rate.

In some implementations, as shown in FIG. 6B, the number of ringopenings can be more than three. For example, the ring 146 can have fivering openings, in particular, the ring openings 600B, 605B, 610B, 615B,620B. The ring openings each have a different size. FIG. 6B depicts thering openings 600B, 605B, 610B, 615B as being smaller than the cap plateopening 625B in the cap plate 150. And, the ring opening 620B is largerthan the cap plate opening 625B. In this example, while the cap plateopening 625B is smaller than the largest ring opening 620B, for otherrings in the dispensing system, the largest ring opening may be smallerthan the cap plate opening. For other rings in the dispensing system,one, two, three, four, or all of the ring openings may be smaller thanthe cap plate opening.

While the examples described with respect to FIGS. 3A to 3G indicatethat the controller controls one ring opening to align, misalign, orpartially align with one cap plate opening, in some cases, thecontroller can control a ring opening to align with two or more capplate openings. As shown in FIG. 6C, the ring 146 has three ringopenings 600C, 605C, 610C, and the cap plate 150 has a set 615C of fivecap plate openings. Each of the cap plate openings can have the samesize.

When the ring opening 605C is aligned with the set 615C of the cap plateopenings to dispense powder as shown in FIG. 6C, the ring opening 605Ccan align with three of the cap plate openings of the set 615C. When thering opening 600C is aligned with the cap plate openings, the ringopening 600C can align with one of the cap plate openings of the set615C. When the ring opening 610C is aligned with the cap plate openings,the ring opening 610C can align with five of the cap plate openings ofthe set 615C. The controller can thus control the powder dispensing ratefrom ring 146 based on the number of cap plate openings aligned with oneof the ring openings.

In some cases, the ring 146 only has one opening that can align with allavailable cap plate openings of the set 615C. For example, the ring 146could have only the largest ring opening 610C. Rather than partiallyaligning the ring 146 with a single opening as described with respect toFIGS. 3A to 3G, the controller can control the ring 146 to align thering opening 610C with one or more of the cap plate openings of the set615C. The controller can select the number of cap plate openings alignedwith the ring opening 610C to control the powder dispensing rate throughthe ring 146.

In some implementations, instead of ring openings of varying size withina single ring, the ring 146 could have ring openings of the same size.As shown in FIG. 6D, the ring openings can be arranged into multiplesets 600D, 605D, and 610D of ring openings. Each one of the sets can bealigned with the cap plate opening 615D. In the example depicted in FIG.6D, each of the sets 600D, 605D, 610D have ring openings spaced apartand sized such that alignment with the cap plate opening 615D enablesall of the ring openings to dispense powder through the cap plateopening 615D. To control a powder dispensing rate, the controller cancontrol which of the sets 600D, 605D, 610D to align with the cap plateopening 615D. In some implementations, some of the ring openings withina set can be blocked by the cap plate 150.

While the ring 146 has been described to be contained within or abovethe cap plate 150 or the cap plate 150 has been described to encirclethe ring 146, in some implementations, the ring 146 can surround the capplate 150. In some cases, the cap plate 150, rather than being ahalf-tube, the cap plate is a plate with cap plate openings or a beamwith cap plate openings. In some implementations, the cap plate 150 is afull tube that is encircled by the series of rings 146. For example, asshown in FIG. 6E, the cap plate 150 is a full tube encircled by therotating ring 146. The cap plate includes a set 600E of cap plateopenings, and the ring 146 includes three ring openings 605E, 610E,615E. In contrast to the examples described with respect to FIGS. 3A to3G and elsewhere, in the example of FIG. 6E, when the ring openings605E, 610E, 615E are misaligned with the set 600E of cap plate openings,the ring 146 blocks the powder from being dispensed from the channel136.

In another example, as shown in FIG. 6F, the ring 146 has a singleopening 600F and the cap plate 150 has a single opening 605F. The ring146 also encircles the cap plate 150. The controller can control theamount of the ring opening 600F aligned with the cap plate opening 605Fto control a powder dispensing rate from the ring 146.

These different examples depicted in and described with respect to FIGS.6A to 6F, while not limiting to the scope of the number of combinationspossible with regards to opening size and quantity, illustrate examplesof combinations different sizes and quantities of ring openings and capplate openings.

The dispensing systems described herein (e.g., the first dispensingsystem 116 of FIGS. 1A and 1B) can be operated to provide paralleldispensing of the powder through multiple holes The dispensing systemcan also selectively dispense through a subset of the holes to dispensepowder in a localized area within a layer. The selective dispensing ofthe powder can enable the additive manufacturing apparatus to reducepowder use in cases where the object to be formed does not span theentire build platform. By having individual control of the holes, thedispensing system can rapidly dispense layers of the powder while stillachieving selective dispensing.

Operations of the Dispensing Systems

The dispensing systems described herein facilitate dispensing andcompaction of powder onto the build platform of the apparatus. Referringto FIG. 1A, 1B, the controller 128 can operate the apparatus 100, and inparticular, the dispensing system 116 to control the dispensing andcompacting operations. The controller 128 can receive signals from, forexample, user input on a user interface of the apparatus or sensingsignals from sensors of the apparatus 100. The user input can be CADdata indicative of the object to be formed. The controller 128 can usethat CAD data to determine properties of the structures formed duringadditive manufacturing processes. Based on the CAD data, the controller128 can generate instructions usable by each of the systems operablewith the controller 128, for example, to dispense the powder, to fusethe powder, to move various systems of the apparatus 100, and to senseproperties of the systems, powder, and/or the workpiece 130.

In an example process of dispensing and compacting the powder, referringto FIG. 3A, powder particles are first loaded through the powder hopper131. Referring to FIG. 3B, the powder particles travel through thepowder hopper 131 toward the entrance 142 of the channel 136. The powderhopper 131 can be a reservoir for the powder. During the dispensingoperations, the powder hopper 131 thereby serves as a powder source forthe powder conveyor 140 and the channel 136.

The controller of the apparatus can control the conveyor drive mechanism139 to drive the powder conveyor 140. As the powder conveyor 140 isdriving, the powder particles at the entrance 142 are conveyed towardthe closed end 144. The powder conveyor 140 can continue conveying thepowder until the powder particles substantially fill the channel 136.

In some implementations, the controller can determine that the powderparticles have substantially filled the channel 136. For example, thecontroller can operate the conveyor drive mechanism 139 in a speedcontrol mode and can determine that a power level exceeding a certainthreshold is indicative of the powder particles having filled thechannel 136. The controller, upon determining that the powder particleshave filled the channel 136, can control an amount of compaction basedon the power level at which the conveyor drive mechanism 139 isoperated. In some cases, the channel 136 can include optical sensors,force sensors, or other appropriate sensors that can detect an amount ofpacking of the powder particles, which can in turn indicate the amountof compaction of the powder particles. The pre-compaction of powder canenable greater uniformity of powder dispensed within and between eachsuccessive layer dispensed onto the build platform by the dispensingsystem 116.

The rings 146, before the controller operates the ring drive mechanisms138, can initially each be set such that their openings 148 are inmisaligned positions relative to the openings 152 of the cap plate 150.In this configuration, powder cannot be dispensed from any of the rings146. When the controller has determined that the powder particles havesubstantially filled the channel 136 and/or has compacted the powderparticles to a desired level of compaction, the controller can operatethe ring drive mechanisms 138, as shown in FIGS. 3C, 3D, and 3E, torotate the rings 146. In particular, the controller can changerotational positions of the rings 146 relative to the cap plate 150 tocontrol a powder dispensing rate from each of the rings 146.

Each ring 146 and its corresponding cap plate openings or opening canhave a configuration of ring openings and cap plate openings, forexample, one of configurations described in examples of FIGS. 6A to 6D.The rings 146 and its cap plate opening or openings may each have aconfiguration that differs from the configuration of the other rings andcap plate openings. The controller can rotate the rings 146 to changethe alignment of the ring openings and the cap plate openings.

The controller, based on, for example, stored data on each of theconfigurations of the rings 146 and the cap plate openings 152, can seta powder dispensing rate from each of the rings 146. The stored data caninclude information pertaining to, for example, sizes, positions, andother geometry of the openings 148 of each of the rings 146 and theopenings 152 of the cap plate. Based on the geometric characteristics ofthe openings 148, 152 and the torque provided by the powder conveyor140, the controller can compute an expected delivery rate of the powderfrom the combination of a particular opening of the rings 146 alignedwith a particular opening of the cap plate 150.

This control of the rotational position of the rings enables thecontroller to set the powder dispensing rate as well as the locationsalong the channel 136 where powder is to be dispensed. The controllercan control the rings 146 such that powder is dispensed from all of therings 146, thus enabling wide parallel dispensing of powder onto thebuild platform of the apparatus. The controller can also control therings 146 such that powder is only dispensed from some of the rings 146.The controller can therefore localize the powder dispensing to occuronly along a portion of the channel 136.

The controller can control the level of compaction, the location ofpowder dispensing, and the rate of powder dispensing based on thedesired levels for each of those parameters included in the CAD data. Inthis regard, the controller can control the ring drive mechanisms 138and the conveyor drive mechanism 139 to achieve these desiredparameters. Furthermore, the controller can use the CAD data, which canspecify the geometry of the object to be formed, to control where thepowder is to be dispensed. While the controller can control a positionof the dispensing system above the build platform to control where thepowder is dispensed, the controller can also control where along thedispensing system the powder is dispensed.

Referring to FIGS. 1A and 1B, the controller can control other systemsto perform operations to form the object. These systems include theprinthead 102, the heat source 112, and the energy source 114 to fusethe powder dispensed by the dispensing system 116. After the dispensingsystem 116 has dispensed a layer of the powder, the controller cancontrol the heat source 112 and the energy source 114 to cooperate toheat and fuse the powder within the layer. The controller can thencontrol the dispensing system 116 to dispense another layer of thepowder.

Controllers and computing devices can implement these operations andother processes and operations described herein. As described above, thecontroller 128 of the apparatus 100 can include one or more processingdevices connected to the various components of the apparatus 100, e.g.,actuators, valves, and voltage sources, to generate control signals forthose components. The controller can coordinate the operation and causethe apparatus 100 to carry out the various functional operations orsequence of steps described above. The controller can control themovement and operations of the systems of the printhead 102. Thecontroller 128, for example, controls the location of feed material,including the first and second powder particles. The controller 128 alsocontrols the intensity of the energy source based on the number oflayers in a group of layers to be fused at once. The controller 128 alsocontrols the location where energy is added by, for example, moving theenergy source or the printhead.

The controller 128 and other computing devices part of systems describedherein can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware. For example, the controllercan include a processor to execute a computer program as stored in acomputer program product, e.g., in a non-transitory machine readablestorage medium. Such a computer program (also known as a program,software, software application, or code) can be written in any form ofprogramming language, including compiled or interpreted languages, andit can be deployed in any form, including as a standalone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment.

The controller 128 and other computing devices part of systems describedcan include non-transitory computer readable medium to store a dataobject, e.g., a computer aided design (CAD)-compatible file thatidentifies the pattern in which the feed material should be depositedfor each layer. For example, the data object could be a STL-formattedfile, a 3D Manufacturing Format (3MF) file, or an Additive ManufacturingFile Format (AMF) file. For example, the controller could receive thedata object from a remote computer. A processor in the controller 128,e.g., as controlled by firmware or software, can interpret the dataobject received from the computer to generate the set of signalsnecessary to control the components of the apparatus 100 to fuse thespecified pattern for each layer.

While this document contains many specific implementation details, theseshould not be construed as limitations on the scope of any inventions orof what may be claimed, but rather as descriptions of features specificto particular embodiments of particular inventions. Certain featuresthat are described in this document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

The printhead of FIG. 1A includes several systems that enable theapparatus 100 to build objects. In some cases, instead of a printhead,an AM apparatus includes independently operated systems, includingindependently operated energy sources, dispensers, and sensors. Each ofthese systems can be independently moved and may or may not be part of amodular printhead. In some examples, the printhead includes only thedispensers, and the apparatus include separate energy sources to performthe fusing operations. The printhead in these examples would thereforecooperate with the controller to perform the dispensing operations.

While the operations are described to include a single size of powderparticles, in some implementations, these operations can be implementedwith multiple different sizes of powder particles. While someimplementations of the AM apparatus described herein include two typesof particles (e.g., the first and the second powder particles), in somecases, additional types of particles can be used. As described above,the first powder particles have a larger size than the second powderparticles. In some implementations, prior to dispensing the secondpowder particles to form a layer, the apparatus dispenses third powderparticles onto the platen or underlying previously dispensed layer.

The processing conditions for additive manufacturing of metals andceramics are significantly different than those for plastics. Forexample, in general, metals and ceramics require significantly higherprocessing temperatures. Thus 3D printing techniques for plastic may notbe applicable to metal or ceramic processing and equipment may not beequivalent. However, some techniques described here could be applicableto polymer powders, e.g. nylon, ABS, polyetheretherketone (PEEK),polyetherketoneketone (PEKK) and polystyrene.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,

-   -   Various components described above as being part of the        printhead, such as the dispensing system(s), spreader(s),        sensing system(s), heat source and/or energy source, can be        mounted on the gantry instead of in the printhead, or be mounted        on the frame that supports the gantry.    -   The dispensing system(s) can each include two or more powder        conveyors, e.g., two or more screw conveyors or auger conveyors.    -   The cap plate can include a drive mechanism that rotates the cap        plate relative to the rings. In some cases, the cap plate can        translate relative to the rings. Movement of the cap plate        relative to the rings can further facilitate alignment and        misalignment of the openings of the rings and the openings of        the cap plate.    -   The cap plate can include nozzles for each of the cap plate        openings that enable a more precise delivery of the powder onto        the build platform.

Accordingly, other implementations are within the scope of the claims.

What is claimed is:
 1. An additive manufacturing apparatus for formingan object, the additive manufacturing apparatus comprising: a platen tosupport the object being formed; a dispensing system overlying theplaten, the dispensing system comprising a powder source configured tohold powder to be dispensed over a top surface of the platen, a powderconveyor extending over the top surface of the platen, the powderconveyor comprising a proximal end configured to receive the powder fromthe powder source, the powder conveyor being configured to move thepowder carried within the powder conveyor along a length of the powderconveyor, a plurality of rings arranged coaxially along a longitudinalaxis of the powder conveyor and forming a tube surrounding the powderconveyor and configured to contain the powder, and each concentric ringcomprising at least one ring opening; and a cap plate extending along alength of the tube, the cap plate comprising at least one cap plateopening wherein each ring is configured to be independently rotatablesuch that the at least one ring opening of the respective concentricring is movable into or out of alignment with the at least one cap plateopening, wherein the powder is dispensed from the tube through the atleast one ring opening and the at least one cap plate opening when theat least one ring opening and the at least one cap plate opening arealigned; and an energy source to apply energy to the powder dispensed onthe top surface of the platen to form a fused portion of the powder. 2.The additive manufacturing apparatus of claim 1, wherein the powderconveyor is rotatable about the longitudinal axis to move the powdercarried within the powder conveyor along the length of the powderconveyor.
 3. The additive manufacturing apparatus of claim 2, whereinthe powder conveyor further comprises a screw conveyor coaxial with thelongitudinal axis of the powder conveyor and rotatable about thelongitudinal axis of the powder conveyor such that, when the screwconveyor rotates, the screw conveyor moves the powder carried within thepowder conveyor along the length of the powder conveyor.
 4. The additivemanufacturing apparatus of claim 3, wherein: the screw conveyor isconfigured such that when the screw conveyor rotates in a firstdirection about the longitudinal axis, the screw conveyor carries thepowder along the longitudinal axis away from the proximal end of thepowder conveyor and when the screw conveyor rotates in a seconddirection about the longitudinal axis, the screw conveyor carries thepowder along the longitudinal axis toward the proximal end of the powderconveyor.
 5. The additive manufacturing apparatus of claim 4, comprisinga motor to drive the screw conveyor and a controller coupled to themotor, wherein the controller is configured to cause the screw conveyorto alternate between rotation in the first direction and the seconddirection during dispensing of the powder to form the object.
 6. Theadditive manufacturing apparatus of claim 4, wherein the screw conveyoris configured to compact the powder when the screw conveyor rotates inthe first direction.
 7. The additive manufacturing apparatus of claim 4,wherein a controller is configured to cause the screw conveyor to, priorto the dispensing, rotate in the first direction until powder extendsalong substantially all of the tube.
 8. The additive manufacturingapparatus of claim 1, wherein each ring comprises a plurality ofpositions spaced angularly around the ring, each position having one ormore openings and having a distinct combination of a number of openingsand opening size.
 9. The additive manufacturing apparatus of claim 8,wherein each ring is movable between the positions such that a differentposition is aligned with the at least one cap plate opening.
 10. Theadditive manufacturing apparatus of claim 8, wherein the combinationfurther defines the at least one cap plate opening of each concentricring, the combination further comprising a number of openings of and aposition of the at least one cap plate opening for each concentric ring.11. The additive manufacturing apparatus of claim 1, wherein a distalend of the powder conveyor extends over the top surface of the platenand is closed to prevent the powder from exiting the powder conveyorthrough the distal end.
 12. The additive manufacturing apparatus ofclaim 1, wherein the at least one cap plate opening comprises a slotextending along a longitudinal axis of the cap plate.
 13. The additivemanufacturing apparatus of claim 1, wherein the at least one cap plateopening comprises a plurality of openings for each ring.
 14. Theadditive manufacturing apparatus of claim 1, wherein the tube surroundsthe cap plate.
 15. The additive manufacturing apparatus of claim 1,wherein the cap plate surrounds the tube.
 16. The additive manufacturingapparatus of claim 1, wherein a drive system of each concentric ringcomprises: a motor with a rotational axis offset from and parallel tothe longitudinal axis of the powder conveyor, and a linkage systemconnected to the motor such that rotation of the motor about itsrotational axis causes rotation of the concentric ring about thelongitudinal axis of the powder conveyor.
 17. The additive manufacturingapparatus of claim 16, wherein the motor of the drive system of each ofthe plurality of rings comprises a distinct shaft length.
 18. Theadditive manufacturing apparatus of claim 1, wherein a drive system ofeach concentric ring comprises a solenoid configured to generate anelectromagnetic field to rotate the concentric ring about thelongitudinal axis of the powder conveyor.
 19. The additive manufacturingapparatus of claim 1, wherein: the dispensing system is a firstdispensing system, the powder is a first powder, the additivemanufacturing apparatus further comprises a second dispensing systemconfigured to receive a second powder to be dispensed over the topsurface of the platen, and the second powder comprises adiameter—smaller than a diameter of the first powder.
 20. The additivemanufacturing apparatus of claim 1, wherein the energy source comprisesa plurality of heaters configured to apply the energy to the powder, theplurality of heaters being addressable such that that the energy isselectively applied to the powder dispensed through the at least onering opening and the concentric at least one cap plate opening.
 21. Adispensing system comprising: a powder source configured to hold powderto be dispensed over a top surface of a platen; an powder conveyorextending over the top surface of the platen, the powder conveyorcomprising a proximal end configured to receive the powder from thepowder source, the powder conveyor being configured to move the powdercarried within the powder conveyor along a length of the powderconveyor; a plurality of rings arranged coaxially along a longitudinalaxis of the powder conveyor and forming a tube surrounding the powderconveyor and configured to contain the powder, and each concentric ringcomprising at least one ring opening; and a cap plate extending along alength of the tube, the cap plate comprising at least one cap plateopening wherein each ring is configured to be independently rotatablesuch that the at least one ring opening of the respective concentricring is movable into or out of alignment with the at least one cap plateopening, wherein the powder is dispensed from the tube through the atleast one ring opening and the at least one cap plate opening when theat least one ring opening and the at least one cap plate opening arealigned.